There are currently three calcium antagonist drugs--verapamil, diltiazem, and nifedipine---being investigated for clincal use in the treatment of angina. Although each shares a common mechanism (inhibits calcium entry into cells) they appear to have different physiologic effects and potencies on the heart and blood vessels. This study definitely examined this question and demonstrated that at doses causing equal decreases in blood pressure verapamil, diltiazem, and nifedipine had markedly different effects on muscle contraction: nifedipine increased contraction, verapamil decreased contraction and diltiazem had no change. These differences will have important clinical implications in choosing one of these drugs for a particular patient.